Fluid contact coking of hydrocarbon oils



June 16, 1959 T. WILLIAMSON FLUID CONTACT COKING OF' HYDROCARBON OILIS Filed Nov. 29, 1954 RNN mwN

United States Patent Ofice 2,890,998 Patented June 16, 1959 FLUID CONTACT COKING OF HYDRO- CARBON OILS Tom Williamson, Arlington, Va., assigner to Texaco Inc., a corporation of Delawaige This invention relates to the cracking and coking of hydrocarbonoils in contact with highly heated powdered or pulverulent coke under fluidized conditions In this type of process coke from the reactor has been subjected to combustion to burn a portion of the coke and the heated coke returned to the reactor. Such a process requires an expensive compression step to compress the air sufficiently to effect a desirable rate of burning and, furthermore, involves the destruction of a portion of the coke formed in the process. The present invention eliminates the coke burning step and avoids the necessity of air compressors. In accordance with the invention the coke ,from the tluid contacting zone is fluidized with steam yand the fluent mixture passed thru a separate heater wherein it is heated to a temperature above that obtaining in the reaction zone and resultant heated eliiuent from the heater delivered to the reaction zone -to maintain the desired coking temperature therein.

ln practicing the invention Ka heavy stock, such as reduced crude or other residual stock, is delivered to the coking and cracking reaction zone wherein it is contacted with hot iluidized coke which quickly raises the temperature to the desired cracking and coking temperature. Coke is Withdrawn from the reaction Zone and is transported by steam to a separate externally red tubular heater wherein the steam-coke mixture is heated to a suicien-tly high temperature to support the coking in the reaction zone and the heated coke is recycled to the reaction zone. 'Ihe process is self-contained as regards the coke used in the contacting reaction zone, that is, after an initial charge of coke in starting a run, suicient coke `is produced to continue the contacting operation.

A feature of the invention is the withdrawal of product `coke at the point of maximum temperature in the cycle as between the reactor and the coke vand steam heater. The heated stream from the latter heater is directed to a separator from which the separated steam is delivered to the reactor to maintain iiuidized conditions therein. A portion of the separated coke is delivered to the reactor and the other lportion is removed from the cycle as product coke.

For the purpose of more Ifully explaining the invention reference is now had to the accompanying drawing which is a diagrammatic elevational flow diagram illustrating a preferred embodiment of the invention.

The charging stock is preheated in a heating coil and is delivered through a transfer line 11 to a coking chamber 12 preferably through a distributor 13 by which the oil is latornized or distributed into contact with the coke particles maintained under liuidized conditions therein. The gaseous amd vaporous products of reaction are taken off overhead, preferably through a conventional separator or cyclone (not shown), and are directed through a line 14 to fractionating equipment for making such separations of products as may be desired.

Coke particles from the dense tluidized bed in the reactor descend through a leg or standpipe 15 and steam introduced through a line 16 aspirates the coke passing from the leg 15 and the mixture or dispersion of steam and coke is transported through a line 17 to a tubular heater 18 which is positioned in a furnace 19. The tubular heater is vertically disposed and provided with an oil or gas burner 19a. The coke-steam mixture is heated suiiiciently lto maintain the desired cracking land coking conditions in the coke contacting chamber 12.

The heated stream of coke and steam passes through a -line 20 to a separator or de-steamer 21 to effect a separation of coke particles from steam. The separated steam is delivered through a line 22 to a lower portion of the coking chamber 12 to supply heat and to maintain iluidization therein. The separated coke descends through leg 23 provided with a branch 4line 24 by which coke is supplied to the coking drum 12 preferably at a point in the dense bed therein and with a second branch line 25 by which that portion of the coke desired to be removed as product is withdrawn from the cycle of operations.

Steam for the process is superheated in exchanger 26 which receives heat from flue gases from the furnace 19 and the superheated steam is delivered through line 27 thence through branch line 16 for dispersing and transporting coke `from the reactor as has been explained. An additional branch line 28 supplies stripping steam to the leg 15 and a branch line 29 supplies steam to the transfer line 11 for mixing with the charging stock to the reactor.

Normally the coke Withdrawn through line 25 has a suiciently volatile content for most purposes but when it is desired to produce a coke of exceptionally low volatile content the coke in line 25 may be delivered to a calciner 30 and ue gas and air is admitted through line 3l to effect burning of coke and produce a very low volatile content coke. The calcined coke product is withdrawn though -line 32. Flue gases from the calciner pass through Iline 33 to the furnace 19 to supply additional heat thereto. Thus, it is only the product coke which in any case is subjected to combustion. The product coke ordinarily constitutes a very small proportion, as some l0 to 15%, of the total coke in the cycle of operations.

The process is adapted particularly for the processing of heavy residual stocks such as reduced crude. In practicing the invention the heavy charge stock is heated in the coil 10 to a temperature of about 780 F. or higher for delivery to the coking chamber. The iiuent mixture of steam and coke is heated in the tubular heater 18 to temperatures of the order of 1100" F. and 1200 F. and temperatures such as 900 F. and 100D F. are maintained in the coking chamber 12. The process is advantageously conducted under pressures approximating atmospheric, such as about l0 p.s.i.g., although higher pressures may be used if desired.

Obviously, many modilications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

l claim:

l. In the cracking and coking of hydrocarbon oils, the process that comprises feeding the oil into a reaction zone wherein the oil is contacted with a fluidized mass of coke particles at coking temperature and conversion to lighter hydrocarbons and coke elfected, withdrawing coke particles from said reaction zone, dispersing the withdrawn coke particles in a stream of steam, passing the stream of steam and dispersed coke particles as a confined stream through an indirect heat exchange zone, heating said confined stream by indirect heat exchange in said indirect heat exchange zone to a temperature above Ithat obtaining in said reaction zone, directing the heated stream of steam and coke to Va separation zone Y wherein coke particles are separated from steam, delivering the separated steam to the bottom of said reaction zone to maintain fluidized conditions therein, directing a portion of the separated coke particles `to the iiuidized mass of coke particles in said `reaction zone, passi-ng the remaining portion of said separated coke from said separation zone to a burning zone in contact with a combustion gas comprising air producing a coke of reduced volatile content, and withdrawing coke of reduced volatiie content from said burning zone as product coke.

2. The process of claim 1 wherein gaseous products of combustion are withdrawn from said burning zone and passed in indirect heat exchange with said stream of steam and dispersed coke particles.

References Cited in the le of this patent UNITED STATES PATENTS 2,707,762 Watson May 3, 1955 2,731,400 Jahnig et a1. Jan. 17, 1956 2,731,508 Jahnig et al Ian. 17, 1956 2,734,853 Smith etal. Feb'. 14, 1956 2,813,916 Boston Nov. 19, 1957 FOREIGN PATENTS 1,062,587 France Dec. 9, 1953 

1. IN THE CRACKING AND COKING OF HYDROCARBON OILS, THE PROCESS THAT COMPRISES FEEDING THE OIL INTO A REACTION ZONE WHEREIN THE OIL IS CONTACTED WITH A FLUIDIZED MASS OF COKE PARTICLES AT COKING TEMPERATURE AND CONVERSION TO LIGHTER HYDROCARBONS AND COKE EFFECTED, WITHDRAWING COKE PARTICLES FROM SAID REACTION ZONE, DISPERSING THE WITHDRAWN COKE PARTICLES IN A STREAM OF STEAM, PASSING THE STREAM OF STEAM AND DISPERSED COKE PARTICLES AS A CONFINED STREAM THROUGH AN INDIRECT HEAT EXCHANGE ZONE, HEATING SAID CONFINED STREAM BY INDIRECT HEAT EXCHANGE IN SAID INDIRECT HEAT EXCHANGE ZONE TO A TEMPERATURE ABOVE THAT OBTAINING IN SAID REACTION ZONE, DIRECTING THE HEATED STREAM OF STEAM AND COKE TO A SEPARATION ZONE WHEREIN COKE PARTICLES ARE SEPARATED FROM STEAM, DELIV- 